I put a Pioneer K05 DVD burner in my iBook. I just don't want the hassle of carrying around another piece of equipment. I can't remember how much I paid for it...but it was less than 90 bucks. It does dual layer...and is natively recognized under Tiger. I wouldn't recommend it for the faint of heart...but if you're decent with electronics and don't have parkinson's or some other inability to control your fine motor skills...then it's really not that bad of a process to replace the optical drive in an iBook. Just follow the instructions over at ifixit.com and you should be good to go.
For what it's worth...Newegg's got the K-06 (which also does DVD-RAM) for less than 90 bucks
here.
I've got half a mind to order it and replace mine